Legend:

The electivity (selection index) describe a predator’s preference for prey. It scales from -1 to 1; where -1 indicates total avoidance of a prey; 0 indicates that a prey is taken in proportion to its abundance in the ecosystem; and 1 indicates total preference for a prey. The electivity values are highlighted using a colour scale for the background, scaling from –1 (white) to 1 (red) using shades of red for intermediate values. The electivity index displayed is the standardized forage ration of Chesson (1983), see below.

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The electivity (selection index) describe a predator's preference for prey. It scales from -1 to 1; where -1 indicates total avoidance of a prey; 0 indicates that a prey is taken in proportion to its abundance in the ecosystem; and 1 indicates total preference for a prey. The electivity values are highlighted using a colour scale for the background, scaling from -1 (white) to 1 (red) using shades of red for intermediate values. The electivity index displayed is the standardized forage ration of Chesson (1983), see below.

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One of the most widely used indices for selection is the Ivlev electivity index, ''E,,i,,'' (Ivlev 1961) defined for a group (''i'') as:

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''E,,i,, = (r,,i,, – P,,i,,) / (r,,i,, +P,,i,,)''

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''E,,i,, = (r,,i,, - P,,i,,) / (r,,i,, +P,,i,,)''

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where ''r,,i,,'' is the relative abundance of a prey in a predator's diet and ''P,,i,,'' is the prey's relative abundance in the ecosystem. E''i'' is scaled so that ''E,,i,,'' = -1 corresponds to total avoidance of, ''E,,i,,'' = 0 represents non-selective feeding on, and ''E,,i,,'' = 1 shows exclusive feeding on a given prey'' i''. Note that within Ecopath, ''r,,i,,'' and ''P,,i,,'' refer to biomass, not numbers.